The present invention is generally directed to polythiophenes and uses thereof. More specifically, the present invention in embodiments is directed to a class of polythiophenes wherein certain repeating thienylene units possess side chains, such as alkyl, which are arranged in a regioregular manner on the polythiophene backbone, and which polythiophenes are, for example, useful as active semiconductive materials for thin film field-effect transistors (FETs).
Semiconductive polymers like certain polythiophenes, which are useful as active semiconductor materials in thin film transistors (TFTs), have been reported. A number of these polymers have some solubility in organic solvents and are thus able to be fabricated as semiconductor channel layers in TFTs by solution processes, such as spin coating, solution casting, dip coating, screen printing, stamp printing, jet printing and the like. Their ability to be fabricated via common solution processes would render their manufacturing simpler and cost effective as compared to the costly conventional photolithographic processes typical of silicon-based devices such as hydrogenated amorphous silicon TFTs. Moreover, desired are transistors fabricated with polymer materials, such as polythiophenes, referred to as polymer TFTs, with excellent mechanical durability and structural flexibility, which may be highly desirable for fabricating flexible TFTs on plastic substrates. Flexible TFTs would enable the design of electronic devices which usually require structural flexibility and mechanical durability characteristics. The use of plastic substrates together with organic or polymer transistor components can transform the traditionally rigid silicon TFT into a mechanically more durable and structurally flexible polymer TFT design. The latter is of particular value to large area devices such as large-area image sensors, electronic paper and other display media. Also, the selection of polymer TFTs for integrated circuit logic elements for low end microelectronics, such as smart cards, radio frequency identification (RFID) tags, and memory/storage devices, may also greatly enhance their mechanical durability, and thus their useful life span. Nonetheless, many of the semiconductor polythiophenes are not, it is believed, stable when exposed to air as they become oxidatively doped by ambient oxygen, resulting in increased conductivity. The result is larger off-current and thus lower current on/off ratio for the devices fabricated from these materials. Accordingly, with many of these materials, rigorous precautions have to be undertaken during materials processing and device fabrication to exclude environmental oxygen to avoid or minimize oxidative doping. These precautionary measures add to the cost of manufacturing therefore offsetting the appeal of certain polymer TFTs as an economical alternative to amorphous silicon technology, particularly for large area devices. These and other disadvantages are avoided or minimized in embodiments of the present invention.